1. Field of the Invention
The invention relates to an actuator control apparatus that has an actuator for changing a state amount of an internal combustion engine and a sensor for detecting the actual operation position of the actuator and controls the actuator so as to bring the actual operation position of the actuator to a target operation position set based on the operation state of the internal combustion engine. The invention also relates to a method for controlling such an actuator.
2. Description of the Related Art
For example, Japanese Patent Application Publication No. 2006-37787 describes a variable valve mechanism control apparatus that sets the target operation position of the variable valve mechanism corresponding to the maximum target lift of the intake valves based on the engine operation state. This control apparatus detects the actual operation position of the variable valve mechanism using a sensor and determines the actual maximum lift of the intake valves based on the result of detection by the sensor. Then, the control apparatus controls the operation position of the variable valve mechanism such that the actual maximum lift equals the target maximum lift.
When the variable valve mechanism is placed in an abnormal state due to, for example, foreign matter being jammed at movable portions of the variable valve mechanism, degraded oil sticking to the movable portions, and so on, the maximum lift of the intake valves becomes unable to be properly changed in accordance with the operation state of the internal combustion engine.
Therefore, conventionally, whether the operation state of the variable valve mechanism is normal is diagnosed based on the deviation between the target maximum lift and the actual maximum lift of the intake valves, which deviation is obtained from the result of detection by the sensor. Typically, if the deviation between the target maximum lift and the actual maximum lift has continuously been equal to or lower than a predetermined value for a predetermined period or longer, the state of the variable valve mechanism is diagnosed to be normal, and if not, conversely, the state of the variable valve mechanism is diagnosed to abnormal.
Meanwhile, the actual target lift does not change largely in a state where the target maximum lift does not change largely, such as when the internal combustion engine is idling or when the internal combustion engine is running in a steady state. In such a case, the deviation between the actual maximum lift and the target maximum lift may remain equal to or smaller than the predetermined value even if the variable valve mechanism is in an abnormal state (e.g., the response of the variable valve mechanism is excessively low). In such a case, the aforementioned conventional control apparatus would erroneously determine that the variable valve mechanism presently has no abnormalities, that is, that the state of the variable valve mechanism is presently normal, which is a problem.
Although a variable valve mechanism for changing the maximum lift of the valves of an internal combustion engine, which is one of valve characteristics, has been described above, it is to be understood that problems identical or similar to the one described above may occur to various other actuator control apparatuses that change an engine state amount by controlling the actual operation position of an actuator to its target operation position set based on the engine operation state.